Ooh, I hadn't tried that. I would, but unfortunately I'm not in an area where I can pick up a new character. If you are in an area where you can do that, you might want to try saving your current game under a different name and try dropping Aerie and see what happens (then you could get back to the rest of us).

Then again, I'm almost certain someone will pop up soon with an answer to your question and you won't have to go through it.

He won't leave. Its just one of those quirky NPC interactions. The only consequence of him making Aerie his witch is that when Aerie gets heavily wounded/killed he goes nuts and says something about protecting his witch, then tosses himself into battle to protect her..